Sept. 11 (UPI) -- After 12 days, Pennsylvania prison officials on Monday ended a statewide lockdown on all prisons due to staff members getting sick from exposure to synthetic drugs.

Between May 31 and Sep. 1, more than 50 staff members and 33 prisoners reported being sickened and were taken to outside hospitals, state officials said in a statement. Lab results showed the staff and prisoners came into contact with synthetic cannabinoid -- also known as K2 or Spice -- in multiple instances.

The substances were reportedly sent through the mail system and visitors, leading to the statewide shutdown that included suspending mail and visitation to all state prison facilities in Pennsylvania.

All prisoners were restricted to their cells for 24 hours a day throughout the 12-day lockdown.

Pennsylvania Corrections Secretary John Wetzel said the lockdown was a "difficult time for staff who became ill by encountering suspected synthetic drugs while simply performing their jobs.

"It also has been a challenging time for all employees as they were called upon to perform various lockdown-related duties," he added.

The reports of synthetic cannabinoid contamination through the prison mail system led Pennsylvania officials to spend $15 million to increase security, including high-tech body scanners and a digital mail delivery system, the Philadelphia Inquirer reported.

However, the newspaper reported that several toxicologists are skeptical of the validity of the contamination reports and suspect it might be an example of "mass psychogenic illness," in which mass hysteria ensues over the fear of being exposed to a dangerous substance -- or in this case, synthetic marijuana.

"There is some great concern that it's psychogenic," said Jeanmarie Perrone, director of medical toxicology at the University of Pennsylvania's Perelman School of Medicine.

"Mass psychogenic illness happens all the time. We see it all the time with law enforcement," Perrone said. "Police pull someone over and find an unknown substance. Suddenly their heart's racing, they're nauseated and sweaty. They say, 'I'm sick. I'm gonna pass out.' That is your normal physiological response to potential danger."